Survival of Interior Least Tern Chicks Hatched on Gravel-covered Roofs in North Texas

Abstract

Understanding how Interior Least Tern (Sternula antillarum athalassos) chicks hatched on rooftops interact with their environment is essential in the conservation of roof nesting colonies. We observed a colony of terns nesting on gravel roofs in Denton County, Texas, in 2003 and 2004. We used focal sampling to examine how chicks behave in relation to surface temperatures and in the presence of predators. We also placed two types of structures, artificial plants and wooden teepees, on the roofs to determine whether chicks would use them for shade or for protection from predators. As surface temperature increased, chicks increased time spent under cover (whether a man-made structure or being brooded) and decreased intraspecific interactions (ducking while an adult flew over, attacking or being attacked by other terns, submissive behaviors, and posturing). As chicks matured shade use decreased and body maintenance (preening and scratching) increased. When adults were mobbing potential predators over the colony, chicks ceased body maintenance, flight muscle preparation (stretching wings or flapping wings), and intraspecific interaction. Most chicks either fell prostrate where they stood when mobbing began or ran away from the predator. The use of structures by chicks did not change in the presence or absence of potential predators. Of the two experimental structures, only artificial plants were used more than expected. Overall, chicks hatched on roofs survive high surface temperatures by relocating to shade and survive predation by running or using camouflage. Artificial plants may be important for providing shade but not for providing protection against predators.